Plasma Technology. FLCC Workshop & Review September 13, 2006 FLCC

Transcription

1 1 Plasma Technology Professors Jane P. Chang (UCLA), Michael A. Lieberman, David B. Graves (UCB) and Allan J. Lichtenberg, John P. Verboncoeur, Alan Wu, Emi Kawamura, Chengche Hsu, Joe Vegh, Insook Lee (UCB), and John Hoang (UCLA) Workshop & Review September 13, /13/ Plasma

2 09/13/ Plasma 2 Dual/Triple Frequency Capacitive and Inductively Coupled Discharges for Etch Coordinated research involving three PI s Michael A. Lieberman (UCB) - Theory and kinetic (PIC-MCC) simulations David Graves (UCB) - Chemistry, plasma and neutral transport, and transient effects - Fluid simulations (FEMLAB) and molecular dynamics simulations of plasma-surface interactions Jane P. Chang (UCLA) - Profile evolution in Si, SiO 2, porous dielectrics, high-k dielectrics - Feature scale simulations (DSMC) and experiments (SEM)

3 3 Relationships Among the Plasma Projects Lieberman (Theory, PIC-MCC) Electron energy deposition Graves (Fluid and MD) Reactor-scale models Surface-scale simulations Ion energy distribution Ion and neutral fluxes Chang (DSMC) Feature-scale experiments Plasma-surface interactions: molecular dynamics 09/13/ Plasma Feature level profile evolution and control

4 4 Plasma Sources for Feature Level Compensation and Control Workshop & Review September 13, 2006 David B. Graves, Chengche Hsu, Insook Lee, and Joe Vegh UC Berkeley 09/13/ Plasma

5 5 Summary of Research (Graves) Develop 2-D reactor-scale fluid models of multiple frequency capacitive and inductively coupled discharge tools for etch and deposition Focus on development of comprehensive, computationally efficient models that can be coupled to profile simulations (Chang), using kinetic simulation information (Lieberman) and that predict tool/feature uniformity 09/13/ Plasma

6 6 One Dimensional Dual Frequency Fluid Model Results* Argon, p = 50 mtorr, 800 V 27 MHz,, 800 V 2 MHz applied at left electrode 27 MHz 2 MHz 0.02 m * Mark Nierode; ( student; graduated 5-05) 09/13/ Plasma

7 7 Currents at Powered Electrode 09/13/ Plasma

8 8 Neutral Flow Configuration Commercial tools typically feature dual flow configurations to allow for greater process control (e.g. balance fluorocarbon deposition and etching) Investigate the transport of the tuning gas and its effect on reactor chemistry Pressure ~ 30 mtorr 400/20/9 sccm Ar/c-C 4 F 8 /O sccm O 2 09/13/ Plasma

9 9 2-D Capacitive Fluid Models - Electrostatics model (Poisson equation only) - Ignores EM effects - Resolves sheath motion; computationally expensive - Investigated role of radial plasma grounding important effects on plasma uniformity RF RF Case 1 09/13/ Plasma Case 2

10 10 2-D Inductive Plasma Fluid Models* Nonlinear solver u,v,p,t Nonlinear solver w j Linear solver E θ Time dependent solver n i,j, Te No Converged? Yes * Chengche (Jerry) Hsu; ( student; graduated 5-06) 09/13/ Plasma

11 11 2-D Inductive Plasma Fluid Models* 150W ICP power, 10mT pressure, Ar 15 sccm, O sccm, and Cl sccm. * Hsu, Coburn, and Graves, J. Physics D, /13/ Plasma

12 12 2-D Multi-frequency Plasma Fluid Models: EM Effects* Use electromagnetic model in FEMLAB, couple to plasma fluid models for parallel plate electrode geometries Solve Maxwell equations in 2-D axial symmetry Assuming a transverse magnetic (TM) mode having only the magnetic field component H φ ~ e jwt, the Maxwell equations are * Insook Lee Hφ = jωε 0κ per, z 1 ( rhφ ) = jωε 0κ pez, r r Er Ez = jωµ 0Hφ, z r 2 ω pe whereκ p = 1 ω( ω jν 09/13/ Plasma σ p = ε ω 0 2 pe jω + ν en en j = 1 σ p, ) ωε 0

13 13 2-D Multi-frequency Plasma Fluid Models: EM Effects* TM wave launched E new (r,z) = E old (r,z) + E EM Model (E) Plasma Model (n e, T e ) * Insook Lee 09/13/ Plasma n e,new (r,z) = n e,old (r,z) + n e, T e,new (r,z) = T e,old (r,z) + T e

14 14 2-D Multi-frequency Plasma Fluid Models: EM Effects* * Insook Lee 60 MHz, 200 mtorr, 20W, Ar 09/13/ Plasma

15 15 Future Milestones Extend tool-scale reactor simulation to industrially-relevant tool chemistries and geometries, focusing on plasma tool uniformity and electromagnetic power coupling 09/13/ Plasma

16 16 Plasma Sources for Feature Level Compensation and Control Workshop & Review September 13, 2006 Michael A. Lieberman, Allan J. Lichtenberg, John P. Verboncoeur, Alan Wu, Emi Kawamura UC Berkeley 09/13/ Plasma

17 17 Summary of Research (Lieberman) Develop kinetic simulation models of multiple frequency capacitive discharge tools for dielectric etch and deposition Focus on electron energy depositions and ion energy distributions 09/13/ Plasma

18 18 Theory of Dual Frequency Stochastic Heating Theory completed and compared to PIC simulations 1. Sstoc = 0.5mevensmubh (1 + πh l / 4)[ H l /( H l + 2.2)] Kawamura High Frequency limit F ( H l n sm = plasma density at ion sheath boundary. u bh = amplitude of high f bulk oscillation velocity. H l = a normalized low f bulk oscillation amplitude. 2 ) = Low Frequency Enhancement For H l >> 1, H l (V sh /T e ) 1/2. Future goal: Incorporate into 2D reactor-scale (Graves) and into 3D feature-scale (Chang) practical simulators. 1 Kawamura et al., Physics of Plasmas 13, (2006). 09/13/ Plasma

19 19 Multi-Frequency Theory of Ion Energy Distributions Theory developed and compared to particle-in-cell simulations V s (f) V i (f) Apply filter α(f) Wu Fourier Transform Inverse Fourier Transform Sheath Voltage V s (t) Ion response V i (t) Σ dv i /dt -1 IED (shown on next slide) Future goal: Incorporate into 2D reactor-scale (Graves) and into 3D feature-scale (Chang) practical simulators. Improve filter function Address issues of ion-neutral collisions in the sheath and fast neutral generation 09/13/ Plasma

20 20 IED MHz / MHz IED MHz / MHz, 2 MHz 0 Ener gy (ev) Energy (ev) 09/13/ Plasma 1000

21 21 Future Milestones Perform particle-in-cell simulations with dual and/or triple frequency source power to determine ion energy distributions at substrate 09/13/ Plasma

22 22 Feature Profile Evolution during Shallow Trench Isolation (STI) Etch in Chlorine-based Plasmas Workshop & Review September 13, 2006 Jane P. Chang and John Hoang UCLA Special Acknowledgements: Helena Stadniychuk at Cypress 09/13/ Plasma

23 23 Summary of Research (Chang) Feature Scale Modeling Develop a pseudo 3-dimensional simulator based on direct simulation Monte Carlo (DSMC) method Enable process development by shortening experimental time and cost Feature scale model can be coupled to tool scale (Prof. Graves, UCB) Feature scale model can be coupled with PIC/MC model (Prof. Lieberman, UCB) Shallow Trench Isolation (STI) Analyze the outcome of design of experiments in STI etch to correlate experimentally measured parameters with simulation input variables Predict profile evolution during STI etch and confirm simulation with experimental SEM images 09/13/ Plasma

24 24 STI Process ITRS dictates stringent conditions for optimal trench isolation as minimum feature size decreases PR nitride oxide Positive trench tapering angles desired to avoid sharp recesses leading to poly wrap-around Smooth sidewalls needed for less physical and electrical damage Silicon Isolation stack Pattern nitride and strip PR Trench etch Round bottom corners to minimize stress and avoid voids in gapfill tx 1 (nitride) SEM Measured Parameters D 1 D 2 Nitride SWA Sidewall oxidation and deposit trench oxide Desired Properties: CMP planarization Strip nitride and remove pad oxide tx 2 (top Si) tx 3 (bot Si) D 3 Total Si Depth D 4 > D 2 /2 Recess < 0.1 D 2 Curvature: r Si top = r Si bottom = 0.1 D 2 Definitions: D 4 top Si SWA bot Si SWA SWA: sidewall angle; Adapted from ITRS 2003 Thermal Films Supplemental 09/13/ Plasma θ nitride = 90º arctan[(d 1 -D 2 )/2/tx 1 ] θ top Si = 90º arctan[(d 2 -D 3 )/2/tx 2 ] θ bot Si = 90º arctan[(d 3 -D 4 )/2/tx 3 ]

25 25 Correlation between Process and Simulation Parameters Process Parameters Simulation Parameters Chamber Pressure (mtorr) Source Power (W s ) Wafer bias (W b ) DC ratio = I outer /I inner Cl 2 flowrate (sccm) N 2 flowrate (sccm) O 2 flowrate (sccm) Ion Angle Distribution (IAD) Ion Energy Distribution (IED) Mean Ion Energy Cl Neutral to Ion Ratio N to Ion Ratio (in development) O to Ion Ratio (in development) E-Field lines (future plans) Cl 2 N 2 O 2 I outer I inner Pressure Coil Power W s Substrate Bias W s W b 09/13/ Plasma Other simulation parameters defined by elemental assignment of the initial profile Additional simulation parameters defined by different plasma compositions

26 26 Surface Representation and Normal Actual representation Original representation Cell-centered representation Modified Cell-centered rep. (to be implemented) Cells with high Flux Surface Four point check Least Squares Modified Least Squares Mask Silicon Least Squares Normal Position Along Interface 09/13/ Plasma bumps in sloped side walls removed Least Squares Normal Position Along Interface

27 27 Integrating Results from Plasma, Reactor, and MD Simulations Species Conc. from Reactor/Plasma models Source Plane in Feature Evolution Cl + :Cl:Cl 2 :O:O 2 :SiCl 2 n + Vacuum φ Mask (SiN x ) 85º Grazing 75º Grazing Silicon IEDF and IADF from PIC Model Molecular Scale Scattering by MD Ions at Source Plane in Feature Evolution Scattering Function in Feature Evolution C.F. Abrams and D. B. Graves, JVST A 16(5), 3006 (1998) C. Hsu and D. Graves. 09/13/ Plasma A. Wu and M. Lieberman,

28 4 28 Reaction Kinetics for Etching/Deposition Effect of E ion and n/+ ratio 75eV Cl + /Cl Effect of deposition on etching 1.2 e SiCl SiCl + Cl 3 Etching Yield 2 Si Cl ev (Lam TCP) 55eV Cl + /Cl 35eV Cl + /Cl 0.8 Etching Yield Si Cl Cl/Cl + = 120 with SiCl 2 Cl + alone with SiCl Cl Flux Ratio Cl + 4 Selectivity SiCl 2 Flux Ratio + Cl 4 Angular Dependency Poly Poly Yield Oxide Oxide Cl Flux Ratio Ion incident angle φ (degree from normal) + Ar Kinetics affected by ion energy and angle: 09/13/ Plasma Y = c( φ)* A*( Eion Eth )

29 29 Pressure (mt) W s (W) W b (W) DC ratio ID Fractional Factorial DOE for Si Etch Cl 2 (sccm) N 2 (sccm) O 2 (sccm) Chlorination: Sorption of Chlorine ion: Ion-enhanced etching: SiCl 2 Deposition: Oxygenation: Sputtering: Sorption of sputtered Si: Recombination of chlorine: 7 factors, 2 levels, and 16 experiments Pressure (plasma density) and DC ratio had statistically significant effects Need to quantify the effect of oxygen addition DOE to assess the effect of oxygen 09/13/ Plasma Mechanisms considered in simulation Cl Cl s 0 Cl (1 ζ Cl ζ O ) ( g ) + Cl( s) + + Cl c( φ) ( g) ( s) Si + 4Cl SiCl + 4 c( φ) βcl ( s) ( s) 4( g) SiCl 3 0 ssicl 2 + Si + 2 Cl 2( g) ( s) ( s) so 0 (1 ζcl ζo) + O ( g) ( s) Y SP Si Si + () s ( g) s0 + Si Si ( g) ( s) r + Cl ( g) ( s) 2 + ( g) O Si Si Cl Cl Cl Cho, H.S. et al. Mat. Sci. in Semi. Process. 8 (2005) 239 Ulal, S.J et al. J. Vac. Sci. Technol. A 20(2)

30 Cl 2 /N 2 Plasma 30 Simulations vs. Experiments Effect of Chemistry Cl 2 /N 2 /O 2 Plasma º Low density plasma º º º º º Effect of Plasma º º 256 High density plasma º 82.5º Simulated more microtrenching and less tapering in a lower density plasma Identified the effect of neutral-to-ion ratio and IAD 09/13/ Plasma Simulated no microtrenching and much tapered sidewalls due to oxygen addition Assumption for deposition: the etching kinetics for SiO x Cl y similar to SiCl 2

31 31 Low DC ratio Simulations vs. Experiments High density plasma, with O 2 in Cl 2 High DC ratio º º º 85.6º º º High density plasma, with O 2 in Cl 2, low DC ratio Low substrate bias High substrate bias º º º º 87.7º º º More hard mask erosion, resulting in slight bowing Higher etch rate, more hard mask erosion, resulting in slight bowing 09/13/ Plasma

32 32 Year 3 Milestones Year 3: January 27, 2006 ~ January 26, 2007 Quantified the effect of O 2 addition to the etch profile evolution during STI etch Predicted feature profile evolution during STI etch and confirm simulation with experimental measurements Validate the simulation results beyond specially planned DOE results Correlate plasma operating parameters to simulation input profiles to allow a more direct comparison of the simulation results to experimental outcomes 09/13/ Plasma